Safety razors

ABSTRACT

A safety razor blade unit including a guard, a cap, and a group of three blades with parallel sharpened edges located between the guard and cap, the first blade defining a blade edge nearest the guard having a negative exposure not less than −0.2 mm, and the third blade defining a blade edge nearest the cap having a positive exposure of not greater than +0.2 mm, the second blade defining a blade edge having an exposure not less than the exposure of the first blade and not greater than the exposure of the third blade.

This invention is concerned with safety razors, and relates inparticular to safety razors having blade units with a plurality ofblades defining parallel sharpened edges arranged to pass in turn over askin surface being shaved. As well known in the art blade units may bepermanently attached to a razor handle or take the form of detachablecartridges intended to be replaced when the blade edges have becomedulled. In either type of razor the blade unit may be fixed in positionon the handle or pivotable about an axis parallel to the blade edges.The invention disclosed herein is applicable to all these forms of bladeunit.

Safety razors having blade units with two blades have in recent yearsbeen sold in very large numbers and are generally acknowledged to give abetter quality of shave, especially in terms of closeness, than singlebladed razors. Furthermore, over the years there have been many writtenproposals to provide safety razors with several blades. A blade unithaving many blades can produce a closer shave than a similar blade unitwith only one or two blades. However, closeness of shave obtained isonly one parameter by which razor users judge the performance of arazor. Adding extra blades can have a serious detrimental influence onother blade unit characteristics, most notably the drag forcesexperienced when the blade unit is moved over the skin, with theconsequence that the overall performance of the blade unit can bemarkedly inferior despite a closer shave being obtainable. As a result,to our knowledge no razors with blade units incorporating more than twoblades have been successfully marketed to date.

It has been found that with a blade unit comprising three blades, thefrictional drag forces can be kept at an acceptable level while allowingan improved shaving efficiency, by setting the blades relative to eachother and to guard and cap surfaces positioned in front of and behindthe blade edges, according to a particular geometrical disposition.Thus, in accordance with the present invention there is provided asafety razor blade unit comprising a guard, a cap and a group of threeblades with parallel sharpened edges located between the guard and cap,the first blade defining the edge nearest the guard having an exposurenot greater than zero, and the third blade defining the blade nearestthe cap having an exposure not less than zero.

The invention is not limited to blade units in which the blades arerigidly mounted in fixed position relative to the guard and/or cap. Ifthe blades are capable of movement then the geometric parametersstipulated herein are those which apply when the blades are in theirnormal rest positions.

The blade exposure is defined to be the perpendicular distance or heightof the blade edge measured with respect to a plane tangential to theskin contacting surfaces of the blade unit elements next in front of andnext behind the edge. Therefore, for the three-bladed blade unit of theinvention, the exposure of the first or primary blade is measured withreference to a plane tangential to the guard and the edge of the secondblade, and the exposure of the third or tertiary blade is measured withreference to a plane tangential to the edge of the second blade and thecap.

It is preferred that the primary blade has a negative exposure, i.e. islocated below the relevant tangent plane, and the tertiary blade apositive exposure, i.e. is located above the relevant tangent plane.This arrangement has the effect of tending to equalise the workperformed by the respective blades, since in a multiple blade razor theleading blade has a tendency to do most of the work. Of course theexposure of the primary blade must not be so low that it will not makeeffective contact with the skin surface being shaved. The minimumacceptable exposure will be influenced by other blade unit dimensions,such as the distance from the skin engaging surface of the guard to theedge, i.e. “the span” of the primary blade. As referred to herein, “thespan” means the distance from the blade edge to the skin contactingelement immediately in front of that edge as measured along a tangentline extending between the said element and the blade edge. Assuming thespan is not large, i.e. not more than about 1.5 mm, an exposure not lessthan −0.2 mm is satisfactory for the primary blade. For a span of about0.7 mm an exposure of about −0.04 mm has been found to be veryappropriate for the primary blade. With the exposure of the primaryblade being not greater than zero, the span should not be very small anda minimum span of about 0.5 mm is therefore proposed. It is beneficialfor the primary blade span to be smaller than, e.g. approximately halfthe span between the edges of the primary and secondary blades and thespan between the secondary and tertiary blades.

Similarly, practical limitations will establish a maximum acceptableexposure for the tertiary blade. It should not be so great that thetertiary blade carries too high a risk of cutting the skin, for example.It is believed a maximum exposure of around +0.2 mm will ensuresatisfactory results. An appropriate span for the tertiary blade is inthe range of 1.0 to 2.0 mm, which is also applicable to the secondblade.

The exposure of the second or secondary blade is preferably not lessthan the exposure of the primary blade and not greater than the exposureof the tertiary blade. A steadily increasing blade exposure has beenfound most effective. Therefore, the value of the exposure of thesecondary blade is ideally approximately half way between the exposurevalues for the primary and tertiary blades, and very satisfactory testresults have been obtained with all three blade edges lying in a commonplane. In most embodiments a secondary blade exposure substantiallyequal to zero will be very satisfactory. We recommend that the tertiaryblade exposure be a positive value equal in magnitude to the negativeexposure of the primary blade.

Another factor which can influence drag forces associated with theblades is the shaving angle, i.e. the angle between a plane bisectingthe blade tip and the plane with respect to which the blade exposure ismeasured. However, the blade shaving angles are not critical and valueswithin a broad range are acceptable, for example 19-28°. It is notnecessary for all three blades to have the same shaving angles, and themost effective values may depend on the span and exposure selected foreach blade.

With a three-bladed safety razor blade unit having the blades disposedas specified herein we have found an enhanced overall shavingperformance in comparison to a two-bladed razor.

Some specific embodiments of the invention are described below withreference to the accompanying drawings in which:

FIG. 1 shows a schematic representation of a transverse cross-sectionthrough one exemplary embodiment of the invention; and

FIG. 2 shows a schematic representation of a transverse cross-sectionthrough the preferred embodiment of the invention.

In each of FIGS. 1 and 2 there is illustrated a safety razor blade unitintended to be mounted on a razor handle. The blade unit may bepermanently attached to the handle, e.g. in a disposable razor, or maybe formed as a cartridge adapted to be mounted releasably to the handle.In either case the handle forms no part of the present invention and itdoes not need to be described further.

Each of the illustrated blade units has a frame 1 defining a guard 2 anda cap 3. As shown the cap comprises a lubricating strip 4 mounted on theframe. The strip may be of a form well known in the art. Carried by theframe are primary, secondary and tertiary blades 11,12,13 havingparallel sharpened edges. The blades may be supported firmly by theframe to remain substantially fixed in the positions in which they aredepicted (subject to any resilient deformation which the blades undergounder the forces applied against the blades during shaving).Alternatively the blades may be supported for limited movement againstspring restoring forces, e.g. in a downward direction as viewed in thedrawings. The basic construction and assembly of the blade units may beconventional, the novel aspects of the present invention residing in theprovision of three blades set in the blade unit set in particulardispositions with respect to each other and the guard and cap.

In the blade unit of FIG. 1, the edges of all three blades lie in acommon plane P, which plane is also tangential to the skin engagingsurfaces of the guard and the cap and which therefore constitutes the“exposure plane” with respect to which the blade exposures arespecified. In fact the exposure is equal to zero for each of the threeblades 11,12,13. The span S₁ of the primary blade 11 is from 0.5 to 1.5mm and is preferably substantially equal to 0.70 mm. The span S₂ of thesecondary blade 12 and the span S₃ of the tertiary blade 13 have valuesin the range of 1.0 to 2.0 mm. They are shown equal with a valuesubstantially equal to 1.50 mm. The edge of the tertiary blade is at adistance S₄ substantially equal to 1.80 mm in front of the cap. To theextent that the primary blade has zero exposure and the tertiary bladealso has zero exposure, this embodiment shows an arrangement in whichthe exposure values of both blades are at the limit proposed accordingto the present invention. Nonetheless the blade unit will produce verygood shaving results in terms of closeness of shave achieved with anacceptable overall performance taking into account all shavingcharacteristics.

As illustrated in FIG. 1, all three blades have the same shaving angleA, but this is not essential. A more favourable blade arrangement isshown in FIG. 2. The spans S₁,S₂,S₃ and S₄ are the same as thosementioned above for FIG. 1. The primary blade in this embodiment has anexposure of −0.04 mm, the exposure of the secondary blade 12 is zero,the edges of all three blades lying in a common plane P as in FIG. 1,and the exposure of the tertiary blade 13 is +0.06 mm. Thus, there is aprogressive increase in blade exposure from the leading blade 11 to thetrailing blade 13.

With the embodiments of the invention the blade related drag forces towhich the blade unit is subjected in use are reduced by choice of theblade exposure values, but at the same time it is ensured that anenhanced shaving efficiency is secured due to there being threesharpened blades.

What is claimed is:
 1. A safety razor blade unit comprising a guard, acap, and a group of first, second, and third blades with parallelsharpened edges located between the guard and cap, the first bladedefining a blade edge nearest the guard having a negative exposure notless than −0.2 mm, and the third blade defining a blade edge nearest thecap having a positive exposure of not greater than +0.2 mm, said secondblade defining a blade edge having an exposure not less than theexposure of the first blade and not greater than the exposure of thethird blade.
 2. A safety razor blade unit according to claim 1, whereinthe span between the first blade edge and the guard is substantiallysmaller than a span between the edges of the first and second blades andthe span between the edges of the second and third blades.
 3. A safetyrazor blade unit according to claim 2, wherein a span between the firstblade edge and the guard is in the range of 0.5 mm to 1.5 mm.
 4. Asafety razor blade unit according to claim 1, wherein the exposure ofthe first blade is substantially equal to −0.04 mm.
 5. A safety razorblade unit according to claim 1, wherein a span between the edges of thefirst and second blades is substantially equal to 1.5 mm.
 6. A safetyrazor blade unit according to claim 1, wherein a span between the edgeof the third blade and the edge of the second blade is in the range of1.0 to 2.0 mm.
 7. A safety razor blade unit according to claim 1,wherein a span between the edge of the second blade and the edge of thefirst blade is in the range of 1.0 to 2.0 mm.
 8. A safety razor bladeunit according to claim 1, wherein a span between the edges of the firstand second blades and between the edges of the second and third bladesis substantially equal to 1.5 mm.
 9. A safety razor blade unit accordingto claim 1, wherein the span between the edges of the second and thirdblades is substantially equal to 1.5 mm.
 10. A safety razor blade unitaccording to claim 1, wherein the exposure of the second blade issubstantially equal to zero.
 11. A safety razor blade unit according toclaim 1, wherein the exposure of the third blade has a positive valuesubstantially equal in magnitude to the negative value of the exposureof the first blade.